Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers

We have investigated the electrical transport through strained p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement shift for diodes with different well width, the shift due to a central potential spike in a well, and magnetotunnelling spectroscopy demonstrate that the first two resonances are due to tunnelling through heavy hole levels, whereas there is no sign of tunnelling through the first light hole state. This demonstrates for the first time the conservation of the total angular momentum in valence band resonant tunnelling. It is also shown that conduction through light hole states is possible in many structures due to tunnelling of carriers from bulk emitter states.Comment: 4 pages, 4 figure

Gapped and gapless short range ordered magnetic states with (12,12,12)(\frac{1}{2},\frac{1}{2},\frac{1}{2}) wavevectors in the pyrochlore magnet Tb2+x_{2+x}Ti2−x_{2-x}O7+δ_{7+\delta}

Recent low temperature heat capacity (C$_P$) measurements on polycrystalline samples of the pyrochlore antiferromagnet Tb$_{2+x}$Ti$_{2-x}$O$_{7+\delta}$ have shown a strong sensitivity to the precise Tb concentration $x$, with a large anomaly exhibited for $x \sim 0.005$ at $T_C \sim 0.5$ K and no such anomaly and corresponding phase transition for $x \le 0$. We have grown single crystal samples of Tb$_{2+x}$Ti$_{2-x}$O$_{7+\delta}$, with approximate composition $x=-0.001, +0.0042$, and $+0.0147$, where the $x=0.0042$ single crystal exhibits a large C$_P$ anomaly at $T_C$=0.45 K, but neither the $x=-0.001$ nor the $x=+0.0147$ single crystals display any such anomaly. We present new time-of-flight neutron scattering measurements on the $x=-0.001$ and the $x=+0.0147$ samples which show strong $\left(\frac{1}{2},\frac{1}{2},\frac{1}{2}\right)$ quasi-Bragg peaks at low temperatures characteristic of short range antiferromagnetic spin ice (AFSI) order at zero magnetic field but only under field-cooled conditions, as was previously observed in our $x = 0.0042$ single crystal. These results show that the strong $\left(\frac{1}{2},\frac{1}{2},\frac{1}{2}\right)$ quasi-Bragg peaks and gapped AFSI state at low temperatures under field cooled conditions are robust features of Tb$_2$Ti$_2$O$_7$, and are not correlated with the presence or absence of the C$_P$ anomaly and phase transition at low temperatures. Further, these results show that the ordered state giving rise to the C$_P$ anomaly is confined to $0 \leq x \leq 0.01$ for Tb$_{2+x}$Ti$_{2-x}$O$_{7+\delta}$, and is not obviously connected with conventional order of magnetic dipole degrees of freedom.Comment: 7 pages, 3 figure

From Spin Glass to Quantum Spin Liquid Ground States in Molybdate Pyrochlores

We present new magnetic heat capacity and neutron scattering results for two magnetically frustrated molybdate pyrochlores: $S=1$ oxide Lu$_2$Mo$_2$O$_7$ and $S={\frac{1}{2}}$ oxynitride Lu$_2$Mo$_2$O$_5$N$_2$. Lu$_2$Mo$_2$O$_7$ undergoes a transition to an unconventional spin glass ground state at $T_f {\sim} 16$ K. However, the preparation of the corresponding oxynitride tunes the nature of the ground state from spin glass to quantum spin liquid. The comparison of the static and dynamic spin correlations within the oxide and oxynitride phases presented here reveals the crucial role played by quantum fluctuations in the selection of a ground state. Furthermore, we estimate an upper limit for a gap in the spin excitation spectrum of the quantum spin liquid state of the oxynitride of ${\Delta} {\sim} 0.05$ meV or ${\frac{\Delta}{|\theta|}}\sim0.004$, in units of its antiferromagnetic Weiss constant ${\theta} {\sim}-121$ K.Comment: 8 pages, 9 figure

Extending enterprise architecture modeling languages: application to telecommunications service creation

Enterprise Engineering offers a global view on multiple concerns such as processes, stakeholders, supporting technology. This global view is sustained by Enterprise Architecture frameworks, languages, tools and standards. The current effort has been focused on general purpose Enterprise Architecture frameworks, modeling languages and tools, which allow describing a wide range of domains. While they are expressive enough at the business layer, at the technical layer, where more detail is needed to describe a domain specific system, such general purpose Enterprise Architecture Modeling Languages sometime lack the semantic strength required. The concepts present in the language are too abstract, they need refinement and specification. To provide the necessary specific semantic strength, this paper proposes an approach to extend Enterprise Architecture Modeling Languages with domain specificity. The proposed approach is a model-driven one, allowing a high degree of automation in the building of tools for the language extension. To better show its benefits, the approach is applied on the domain of Telecommunications, for defining an Enterprise Architecture Modeling Language extension for service creation. The so defined language and its associated tools are illustrated on an IP Multimedia Subsystem conferencing service example.Vanea Chiprianov, Yvon Kermarrec, Siegfried Rouvrai

Les orientations de valeur des enseignants d'éducation physique et sportive. Influence du sexe, de l'âge et de l'ancienneté

L'objet de cette étude est d'examiner l'influence du genre, de l'âge et de l'ancienneté sur les orientations de valeur d'enseignants d'éducation physique. Les orientations de valeur représentent un système de croyances qui guide les enseignants dans leurs choix de contenus. La version révisée de l'inventaire des orientations de valeur (VOI) a été utilisée pour recueillir les données de 157 enseignants travaillant dans différentes régions de France. Les scores totaux sur chacune des orientations de valeur ont été calculés et utilisés pour diviser les enseignants en deux groupes représentant des catégories de priorités forte et faible. Le test khi-deux a été utilisé pour examiner les données de genre, d'âge et d'ancienneté. Les résultats indiquent que 83 % des enseignants prennent des décisions sur les contenus à enseigner à travers au moins une orientation de valeurs. Il n'y a pas de différences significatives sur le genre, l'âge et, pour quatre orientations de valeur, sur l'ancienneté. Les priorités des enseignants pour le processus d'apprentissage évoluent au cours de leur carrière